Periodic P fertilizer application is recommended for small-holder farmers in Northeast China: evidence from a 12-year study

Phosphorus (P) fertilizer prices rose more than 150 % in the past two decades, thus periodic P fertilization (purchasing and applying superphosphate periodically) could be economically beneficial to small-holder farmers. Still, it is necessary to determine if periodic P fertilization could sustain corn production compared to annual P fertilization. Corn (Zea mays L.) obtains P for its growth and development from soil solution, which is replenished by soil P fractions associated with the soil minerals (inorganic P, Pi) and organic matter (organic P, Po). It is expected that P fertilization regimes (annual vs. periodic applications) will influence the concentration of soil P fractions contributing to corn P nutrition. The objective of the study was to evaluate soil Pi and Po fractions and P uptake in corn agroecosystems of Northeast China under two fertilizer regimes: triple-superphosphate applied annually at 0, 25 or 75 kg P ha(-1), or applied periodically (once every 6 years) as 150 or 450 kg P ha(-1). During the two 6-year periods (1997-2002 and 2003-2008), both periodic and annual triple-superphosphate application significantly (P < 0.05) increased the NaHCO3-Pi (93-453 %), NaOH-Pi (44-135 %) and HCl-Pi (11-45 %) fractions, thus sustaining crop P requirements. Although annual P fertilization gave 35 % more NaHCO3-Pi, 28 % more NaOH-Pi, 15 % greater HCl-Pi and 4 % more crop P uptake at the end of each 6-year period, there was no significant difference in corn yield. Therefore, periodic P application (once in 6 years) is recommended as an economical practice that could lower the cost of P fertilization for small-holder farmers producing corn in Northeast China.